Nanostructured Polymer Films Doped with Cobalt-ferrite Nanoparticles: a Raman Study

July 4, 2017 | Autor: Gustavo Alcântara | Categoria: Raman Spectroscopy, Vibrational Spectroscopy, Optical Properties, Analytical Method
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Nanostructured Polymer Films Doped with Cobalt-ferrite Nanoparticles: a Raman Study Gustavo B. Alcantaraa, Leonardo G. Paternoa, Fernando J. Fonsecab, Emilia C. D. Limac, Paulo C. Moraisa and Maria A. G. Solera a

b

Universidade de Brasilia, Instituto de Fisica, Brasilia-DF 70910-900, Brazil Universidade de São Paulo, EPUSP, Depto de Engenharia de Sistemas Eletronicos, São Paulo-SP 05508-900, Brazil c Universidade Federal de Goias, Instituto de Quimica, Goiania-GO 74001-970, Brazil

Nanocomposites of superparamagnetic iron oxide (SPIO) nanoparticles doped in polymeric matrices have been focus of intensive investigations due to potential applications in EMI shielding, spintronics and sensors.1,2 Apart of several methods, the layer-by-layer (LbL) technique for deposition of ultra-thin films is a simple but yet very powerful approach to produce such nanocomposites once it is capable of providing high control over film thickness and end properties. The LbL technique is based on the sequential adsorption driven by electrostatic attraction of different electrolyte materials, from a liquid phase onto solid substrates. SPIO nanoparticles prepared as either positively or negatively charged species can be sequentially adsorbed with common polyelectrolytes under this methodology. Among different characterization techniques, Raman spectroscopy is very suitable to provide information of the chemical structure of ultra-thin films own to its high sensitivity. SPIO nanoparticles exhibit characteristic Raman scattering modes which are associated to the typical crystalline structure of iron oxide materials. However, in some instances the polymeric matrix can screen the nanoparticle’s presence due to its fluorescence background. In the present study, we employ Raman spectroscopy to investigate the chemical structure of positively-charged cobalt ferrite nanoparticles doped in LbL films of poly(4-sodium styrene sulfonate) (PSS). In addition, transmission electron microscopy (TEM) is employed to evaluate the nanocomposite’s morphology. PSS was purchased from Sigma-Aldrich Co., USA and an aqueous solution (1.8 g L-1, pH 2) was prepared by dissolution in diluted HCl. CoFe2O4 nanoparticles were synthesized by co-precipitation of Co(II) and Fe(III) ions in aqueous alkaline medium according to the method reported previously.3 TEM image of the magnetic fluid (data not show) shows typical spherical nanoparticles with mean diameter of 2.98 ± 0.02 nm. The multilayered nanocomposite films were produced by the electrostatic LbL approach employing CoFe2O4 nanoparticles as cations and PSS as a polyanion. A gold coated glass slide used as substrate was modified with a monolayer of 3-MPA (3-mercaptopropionic acid) prior to film depositions. Substrates were first immersed into the cation’s dispersion for 3 min, then rinsed in a magnetic stirred HCl solution (pH 2) and dried with nitrogen flow. The substrate containing a layer of nanoparticles was subsequently immersed for 3 min into the PSS solution CREDIT LINE (BELOW) TO BE INSERTED ON THE FIRST PAGE OF EACH PAPER CP1267, XXII International Conference on Raman Spectroscopy edited by P. M. Champion and L. D. Ziegler © 2010 American Institute of Physics 978-0-7354-0818-0/10/$30.00

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rinsed and dried as in the nanoparticle layer deposition. The result is a nanoparticle/polyanion bilayer. Multilayered nanocomposite film of (CoFe2O4/PSS)10 was produced by repeating cycles described above. The Raman system (Jobin Yvon Model T64000) was equipped with a charge-coupled device detector. The 514 nm line from an argon ion laser was used to illuminate the sample at an optical power of 0.36 mW. In Figure 1 is presented Raman spectra of the CoFe2O4 nanoparticles powder cast onto the gold-coated glass substrate (a) and (CoFe2O4/PSS)10 nanocomposite film (b). A well-resolved fingerprint of the cobalt ferrite structure is clearly seen in the nanocomposite spectrum, with 5 Raman peaks 328, 499, 558, 619 and 692 cm-1. As to the powder sample a less structured spectrum is observed, although peaks positions are equal in both samples, corresponding to Raman modes characteristic of the cubic inverse spinel Oh7 (Fd3m) space group of CoFe2O4.4

FIGURE 1. Raman spectra of CoFe2O4 powder cast onto the gold-coated glass substrate (a) and (CoFe2O4/PSS)10 nanocomposite film (b).

Nanocomposite films of CoFe2O4 nanoparticle and PSS were produced via the electrostatic LbL technique. One key difference between the protocol we report here and the current literature is that Raman measurements showed that we can get a fingerprint of cobalt ferrite nanoparticles from the nanostructured films without further treatment as annealing.5

ACKNOWLEDGMENTS The financial support from the Brazilin agencies MCT/CNPq, FINEP, CAPES, FUNAPE and FINATEC are gratefully acknowledged. The authors should like to thank Prof. Sonia Nair Bao for TEM measurements.

REFERENCES 1. J. Joo and J. Epstein, Appl. Phys. Letters 65, 2278-2280 (1994). 2. Y. Xu, U. Memmert and U. Hartman, Sens. Actuators A 91, 26-29 (2001). 3. M. A. G. Soler, E. C. D. Lima, S. W. da Silva, T. F. O. Melo, A. C. M. Pimenta, J. P. Sinnecker, R. B. Azevedo, V. K. Garg, A. C. Oliveira, M. A. Novak and P. C. Morais, Langmuir 23, 9611-9617 (2007). 4. T. F. O. Melo, S. W. da Silva, M. A. G. Soler, E. C. D. Lima and P. C. Morais, Surf. Science 18, 3642-3645 (2006). 5. L. B. M. Lopez, J. D. Pasteris and P. Biswas, Appl. Spectrosc. 63, 627-635 (2009).

1167 Downloaded 14 Oct 2010 to 164.41.11.42. Redistribution subject to AIP license or copyright; see http://proceedings.aip.org/about/rights_permissions

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